Embolus blood clot filter with bio-resorbable coated filter members

ABSTRACT

A blood clot filter includes a number of locator members and anchor members, each of the members tipped with a retainer encompassed within bio-resorbable cover material. Upon delivery into a blood vessel, the locator and anchor members position the filter near the vessel centerline. After a period of time, the bio-resorbable cover material resorbs, allowing the retainer on the members to penetrate and attach to the vessel wall. A method of implanting the filter includes delivering the filter into a blood vessel and allowing the bio-resorbable cover material to resorb so retainers on the members can engage the vessel walls.

PRIORITY DATA AND INCORPORATION BY REFERENCE

This is a continuation of U.S. patent application Ser. No. 14/293,246,filed on Jun. 2, 2014, issued as U.S. Pat. No. 9,468,513 on Oct. 18,2016, which is a continuation of U.S. patent application Ser. No.12/096,788, filed on Dec. 29, 2006, issued as U.S. Pat. No. 8,777,975 onJul. 15, 2014, which is a National Stage application under 35 U.S.C. 371of International Application No. PCT/US2006/062730, filed Dec. 29, 2006,which claims the benefit of priority to U.S. Provisional PatentApplication No. 60/754,597, entitled “Embolus Blood Clot Filter withRetainers on Locator Filter Members,” filed Dec. 30, 2005 which isincorporated by reference in its entirety. This invention is related tothe subject matter shown and described in the following: (i) PCTInternational Application No. PCT/US06/62722, filed Dec. 29, 2006,entitled “Removable Blood Clot Filter with Edge For Cutting Through theEndothelium” and claiming the benefit of priority to U.S. ProvisionalPatent Application No. 60/754,600, filed Dec. 30, 2005; (ii) PCTInternational Application No. PCT/US06/62719 filed Dec. 29, 2006,entitled “Embolus Blood Clot Filter with Post Delivery Actuation,” andclaiming the benefit of priority to U.S. Provisional Patent ApplicationNo. 60/754,633, filed Dec. 30, 2005; (iii) PCT International ApplicationNo. PCT/US06/62725, filed Dec. 29, 2006, entitled “Embolus Blood ClotFilter Delivery System,” and claiming the benefit of priority to U.S.Provisional Patent Application No. 60/754,636, filed Dec. 30, 2005; (iv)PCT International Application No. PCT/US06/62720, filed Dec. 29, 2006,entitled “Embolus Blood Clot Filter with Floating Filter Basket,” andclaiming the benefit of priority to U.S. Provisional Patent ApplicationNo. 60/754,599, filed Dec. 30, 2005; and (v) PCT InternationalApplication No. PCT/US06/62733, filed Dec. 29, 2006, entitled “EmbolusBlood Clot Filter Removal System and Method” and claiming the benefit ofpriority to U.S. Provisional Patent Application No. 60/754,598, filedDec. 30, 2005, each of which is hereby incorporated by reference in itsentirety.

TECHNICAL FIELD

This invention relates to a filter device that can be placed in a bloodvessel to reduce the risk of embolisms. More particularly, thisinvention relates to a blood clot filter having anchoring and locatingmembers in which at least one of the members has a portion covered witha bio-resorbable material to provide a delayed engagement between themember and a blood vessel wall.

BACKGROUND ART

In recent years, a number of medical devices have been designed whichare adapted for compression into a small size to facilitate introductioninto a vascular passageway and which are subsequently expandable intocontact with the walls of the passageway. These devices include, amongothers, blood clot filters which expand and are held in position byengagement with the inner wall of a vein, such as the vena cava. Venacava filters are known in the art as described, for example, in U.S.Pat. Nos. 4,425,908, 5,669,933 and 5,836,968, and European Patent Officepublication 0 188 927 A2, each of which are incorporated by referenceherein in their entirety. Such filters may include structure to anchorthe filter in place within the vena cava, such as elongated diverginganchor members with hooked ends that penetrate the vessel wall andpositively prevent longitudinal migration within the vessel. Suchfilters also may include locator structures to position the filterwithin the blood vessel, particularly with respect to the centerline ofthe vessel. Such locator structures may consist of a number of memberswhich press against the walls of the vessel with approximately equalforce, thus causing the center of the filter to move to the centerlineof the vessel. A filter including anchor members having hooked ends andlocator members is disclosed in U.S. Pat. No. 6,258,026, which isincorporated by reference herein in its entirety.

Referring to FIG. 20, a known expanded blood clot filter 10 isillustrated which is made from sets of elongated metal wires. The wiresare held together at one end by a hub 12 where they may be plasma weldedtogether and to the hub or otherwise joined. In one material phase, thewires, which are made of a shape memory material, can be straightenedand held in a straight form that can pass through a length of fineplastic tubing with an internal diameter of approximately 2 mm (No. 7French diameter catheter). At a defined temperature, the filter 10recovers a preformed filtering shape as illustrated by FIG. 20.Similarly, wires of spring metal can be straightened and compressedwithin a catheter or tube and will diverge into the filter shape of FIG.20 when the tube is removed. The blood filter 10 is typically deliveredinto a subject's blood vessel by being pushed out of a catheterpositioned within the vein.

In its normal expanded configuration or preformed filtering shape,illustrated in FIG. 20, filter 10 is a double filter, having a firstforwardly disposed filter basket 14 at the forward or leading end of thefilter and a second forwardly disposed filter basket 16. The two filterbaskets provide peripheral portions which can both engage the inner wallof a blood vessel at two longitudinally spaced locations, and the twofilter baskets are generally symmetrical about a longitudinal axispassing through the hub 12.

The first filter basket 14 is formed by the anchor members 30, with upto twelve circumferentially spaced curved or linear wires forming theanchor members, which extend away from hub 12 and away from thelongitudinal axis of the filter 10 and end in hooks 40, such as thoseillustrated in FIG. 21. The outwardly oriented hooks 40 generally lie ona circle at the maximum divergence of the anchor members 30. Six anchormembers 30 are shown in FIG. 20. The anchor members may be of equallength, but normally the lengths differ so that the hooks 40 will fitwithin a catheter without becoming interconnected. The anchor members 30may be much longer than the locators 20. In the expanded configurationshown in FIG. 20, the anchor members 30 are at a slight angle to thevessel wall, preferably within a range of from ten to forty-fivedegrees, while the hooks 40 penetrate the vessel wall to secure thefilter against movement.

The second filter basket 16 is formed by locators 20 that extendangularly with respect to the longitudinal axis, outwardly and thendownwardly from the hub 12 toward the forward end of the filter 10. Asis shown in FIG. 20, each locator 20 may have a first locator section 21which extends angularly out from the hub 12 to a shoulder 22, and anouter locator section 24 that extends angularly from the shoulder towardthe forward end of the filter. Typically, there are six locators 20 ofequal length extending radially outward from the hub 12 andcircumferentially spaced, such as for example by sixty degrees of arc.

The anchors 30 may be radially offset relative to the locators 20 andmay be positioned halfway between the locators 20 and also may becircumferentially spaced by sixty degrees of arc as shown in FIG. 22.Thus the combined filter baskets 14 and 16 can provide a wire positionedevery thirty degrees of arc at the maximum divergence of the filtersections. With reference to the direction of blood flow, filter basket14 forms a first concave opening toward the leading end of filter 10 andfilter basket 16 forms a second concave opening toward the leading endof filter 10 downstream of filter basket 14.

For a filter to properly deploy the first and second filter basketswithin the blood vessel, it is preferred that the filter hub 12 bepositioned substantially along the centerline of the vessel. Thiscentering function is performed by the locator members which have outerlocator sections 24 that lie on a circle at their maximum divergence andengage the wall 17 of a vessel (preferably at an angle within a range offrom ten to forty-five degrees) to center the hub 12 within the vessel.This is illustrated in FIG. 22. When positioned within a blood vessel,the locator members apply radial pressure to the walls, thereby pushingthe filter hub 2 toward the vessel centerline. When a filter 10, such asthat illustrated in FIG. 20, is ejected from an insertion catheterhub-end first, the locator members 20 will deploy first. Since theas-deployed radial separation between locator tips is larger than thediameter of the blood vessel, the locator tips contact and push againstthe walls of the blood vessel, as illustrated in FIG. 22, therebycentering the filter in the blood vessel before the anchor membersdeploy from the delivery catheter. In addition to serving as filterelements for catching blood clots, this centering function is animportant function of the locator members.

Blood filters which use locator members as described above suffer fromthe disadvantage that the locator members do not contribute to anchoringthe filter longitudinally in the blood vessel. This is because thelocator members must be able to move with respect to the vessel wallwhile the filter centers in the blood vessel. If the locator membersincluded hooks, they could hook into the vessel walls before the filtercenters, leaving the filter in a cocked position. Accordingly, there isa need for a filter that includes hooks on locator members which hookinto the vessel wall after the filter is centered in the blood vessel.

SUMMARY OF THE INVENTION

The various embodiments provide a blood filter that includes locatormembers with a retainer member disposed thereon. In order to permit thelocator members to reposition the filter toward the centerline of theblood vessel during implantation, the retainers are covered orencompassed in a bio-resorbable material. The covered retainers are ableto slide along the endothelial layer of the blood vessel as the filtermoves to a centerline position. After the filter has been positioned inthe blood vessel for a period of time, the bio-resorbable materialcovering the retainer is resorbed by the body, uncovering the retainersso that the retainers can engage the vessel walls, thereby helping tohold the filter in position within the vessel.

The various embodiments further provide a method of securing a bloodfiltering device within a blood vessel wherein a filter with retainermembers covered by a bio-resorbable material position the filter nearthe centerline of the blood vessel. After a period of time, thebio-resorbable material is resorbed by the body, allowing the retainermembers to engage vessel walls.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate presently preferred embodimentsof the invention, and, together with the general description given aboveand the detailed description given below, explain features of theinvention.

FIG. 1A is a cross sectional view of an anchor member covered withbio-resorbable material in place in a blood vessel.

FIG. 1B is a cross sectional view of the anchor member shown in FIG. 1Aafter the bio-resorbable materials has resorbed.

FIG. 1C is a cross sectional view of the sharp tip end of the hook ofFIG. 1A being partially exposed.

FIG. 1D is a cross sectional view of an anchor member in the form of acurved hook deformed into a straightened configuration and maintained inthis configuration by an encapsulation material.

FIG. 2 is a side elevation view of an expanded blood clot filteraccording to an embodiment.

FIGS. 3A and 3B are side elevation views of a retainer for a member ofthe filter of FIG. 2 showing embodiments of the bio-resorbable material.

FIG. 4 is a side elevation view of an expanded blood clot filteraccording to another embodiment.

FIG. 5 is a top down perspective view of an embodiment of a removableblood filter before bio-resorbable material has been applied to theretainers.

FIG. 6 is a bottom up perspective view of the embodiment of FIG. 5.

FIG. 7 is a plan view of the filter of FIG. 5 on longitudinal axis A.

FIG. 8 is a side view of the filter of FIG. 5 viewed along axisVIII-VIII in FIG. 7.

FIG. 9 is a side view of one locator member of the filter of FIG. 5.

FIG. 10 is a side view of the filter of FIG. 5 viewed along axis X-X inFIG. 7.

FIG. 11 is a side view of one anchor member of the filter of FIG. 5.

FIG. 12 is a close up side view of a hook of the anchor member for thefilter of FIG. 5.

FIG. 13 is a side view of the filter of FIG. 5 after bio-resorbablematerial has been applied to the retainers on the locator members.

FIG. 14 is a side view of the filter of FIG. 5 after bio-resorbablematerial has been applied to the retainers on the locator members andanchor members.

FIG. 15 illustrates another embodiment filter that includes a retrievinghook.

FIGS. 16-19 are detail views of a retrieving hook according to thefilter embodiment of FIG. 15.

FIG. 20 is a side elevation view of a prior art expanded blood clotfilter.

FIG. 21 is a side elevation view of a hook for use with the filter ofFIG. 20.

FIG. 22 is an end view of the filter of FIG. 20 in place in a bloodvessel.

MODE(S) FOR CARRYING OUT THE INVENTION

The various embodiments will be described in detail with reference tothe accompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings and this specification to refer tothe same or like parts.

As used herein, the terms “about” or “approximately” for any numericalvalues or ranges indicates a suitable dimensional tolerance that allowsthe part or collection of components to function for its intendedpurpose as described herein. Also, as used herein, the terms “patient,”“host” and “subject” refer to any human or animal subject and are notintended to limit the systems or methods to human use, although use ofthe subject invention in a human patient represents a preferredembodiment.

In one preferred embodiment of a blood filter, locator members 20 arepreferably tipped with a retainer such as, for example, a hook 40. Thepreferred locator members 20 can thus contribute to holding the filterin place within the blood vessel as well as locating the filter withrespect to the body vessel, as illustrated in FIGS. 1A and 1B. In orderto permit the hooked locator members 20 to move over the walls of theblood vessel 17 during the repositioning motion of aligning the filternear the blood vessel centerline, at least the tip portion of eachretainer 40 is covered with a bio-resorbable material. Thebio-resorbable material forms a smooth surface, or at least covers thepoint of the hook for a period of time until after the filter iscentered in the vessel. Although a hook 40 is shown as a preferredembodiment of the retainer for the filter members, other forms of aretainer can be utilized to secure the members to the vessel wall suchas, for example, a projection with a barb formed on the projection or atip with two barbs formed proximate the tip.

Forming a blood clot filter of a Nitinol alloy material, such as Nitinolwire, can facilitate insertion of the filter into a delivery catheterand subsequent expansion of the filter within a vascular or otherpassageway. Although the filters of the various embodiments arepreferably formed from a temperature responsive super-elastic shapememory material, such as Nitinol, they can also be formed of acompressible spring metal such as stainless steel or a suitable plastic.

As illustrated in FIG. 1A, the hook may be covered with a sufficientmass of bio-resorbable cover material 41 to encapsulate the tip of theretainer 40 and present a smooth surface for sliding along the inside ofthe vessel 17. Also, by having a larger surface area for contact withthe vessel wall, as opposed to a point contact or line contact of thelocator member, it is believed that the vessel will suffer less traumaas a result of filter placement. For further delayed uncovering of theretainer, a further coating or additional mass may be employed topostpone the complete dissolution of the cover material 41.Alternatively, a different, slower resorbing material may be used forthe cover material 41.

In an alternative embodiment, as shown in FIG. 1C, the material 41 maycover only a portion of the retainer 40 while leaving a tip exposed. Byhaving the tip exposed, the locating and anchoring functions can stillbe adequately achieved without employing the full anchoring ability ofthe retainer 40.

In a further alternative embodiment, the retainer 40 can be configuredso as to provide positive engagement of the retainer to the vessel wallafter an encapsulation material 41 has been resorbed. As shown in FIG.1D, the retainer 40, which is in the form of a curved hook is deformedinto a generally linear configuration and encapsulated in material 41 soas to maintain the hook in this deformed condition. As the material 41is resorbed, the hook seeks out its original curved configuration. Thisreflex motion of the hook causes the hook to dig further into the vesselwall as more and more of the material 41 is resorbed. In anotherembodiment, instead of having the material 41 entirely covering the tipof the retainer, the material 41 can be a non-resorbable material thatallows for creep of the non-resorbable material (e.g., polyurethane)under an internal stress provided by the deformed hook. By allowing forcreep of the material, the deformed hook would tend to straighten overtime so as to permit the exposed tip to penetrate through the polymerand into the vessel wall.

Referring to FIG. 2, a filter according to the various embodiments mayhave a configuration similar to that of conventional filters, asdescribed above, with the addition of bio-resorbable cover material 41positioned over retainers 40 on the locator members 20. Alternatively,conventionally covered locator members 20 not having a retainer memberor hook can also be covered with a bio-resorbable material to delaydirect engagement of the end of the locator member 20 with the bloodvessel wall for a period of time, preferably until after the filter iscentered in the vessel.

The amount of bio-resorbable material covering a retainer 40 may vary.As illustrated in FIG. 3A, the bio-resorbable cover 41 may encapsulateonly the tip of the retainer, thereby preventing the tip from puncturingthe blood vessel wall. In another embodiment illustrated in FIG. 3B, thebio-resorbable cover 41 may encompass a large fraction or all of theretainer 40. In either of the embodiments illustrated in FIGS. 3A and3B, the cover material 41 may be a near solid bead. In an alternativeembodiment, the cover material 41 may be in the form of a hollow sphereor bead, thereby encompassing at least a portion of the hook within ashell of bio-resorbable material. Use of a smaller bead, as illustratedin FIG. 3A, or a thin-walled hollow bead cover 41 may be considered forapplications where relatively rapid uncovering of the retainer isdesired. In such instances, the smaller amount of cover material willresorb faster than a larger and/or solid bead.

In yet another embodiment, the retainers 40 on the anchor members 30 mayalso be encompassed or covered with a bio-resorbable cover material 41so that when the filter is first delivered into a blood vessel, theanchors deploy without driving the hooks 40 into the vessel wall 17.This embodiment may be employed on filters having locator members 20with hooks, as illustrated in FIG. 4, or those without hooks. As withthe previously described embodiment that comprises hooked locatormembers, after the filter has been in the blood vessel for a while, thecover material 41 is resorbed. When the material is resorbed, the anchorretainers 40 are uncovered and penetrate the vessel wall 17 to preventthe filter from being dislodged by blood flow. This embodiment has theadvantage of allowing the filter to be immediately removed afterdelivery without damaging the endothelial layers of the blood vessel.Although FIGS. 4, 14 and 15 show all of the locator and anchor memberretainers encapsulated, it is foreseeable that one could leave retainers40 exposed to promote at least partial retention of the filter withinthe vessel immediately upon implantation.

Materials which break down or dissolve in blood and are assimilated bythe body, i.e., resorbed, at predictable rates are well known in themedical arts and used in a variety of applications. For example,bio-resorbable sutures and staples are commonly used in surgicalprocedures to close internal wounds long enough to permit tissues toheal before being resorbed to reduce the potential for foreign objectrejection and infections. A number of materials are used forbio-resorbable sutures and may be used for the bio-resorbable structuresof the various embodiments. Such materials may be made from naturalmaterials or synthetic polymers. Natural bio-resorbable materialsinclude, but are not limited to, natural collagens, submucosa sheepintestine, plain gut serosa of beef intestine, and collagen beef flexortendon. Natural absorbable materials prepared from mucosa or submucosalof sheep or beef intestines are broken down by enzymatic degradationwithin the cell. Synthetic bio-resorbable materials include, but are notlimited to: Polyglycolic acid Dexon S homopolymer of glycolic acid;Polyglycolic acid Dexon plus homopolymer of glycolic acid coated withpoloxamer 188; Polyglycolic acid Dexon II homopolymer of glycolic acidcoated with potycaprolate; Polyglactine 910 Vicryl copolymerlactideglycolic acid coated with calcium stearate; Polydioxanone PDSpolymer of paradioxanone; Polydioxanone PDS-II modified PDS;Polyglyconate Maxon copolymer of trimethylene carbonate andpolyglycolicacid; and, Polyglecaprone 25 Monocryl copolymer ofe-caprolactone and glycolide. Synthetic bio-resorbable materials arefirst hydrolyzed (hydrolytic degradation) and then metabolized by thecell. When the bio-resorbable material is degraded by hydrolysis thefragments are phagocytized by the enzymatic action of the cells,metabolized and excreted. The bio-resorbable materials can be configuredto be absorbed or degraded within from 2 weeks to 2 years afterimplantation. Other materials can include biodegradable polymers such aspolylactic acid, i.e., PLA, polyglycolic acid, i.e., PGA, polydioxanone,i.e., PDS, polyhydroxybutyrate, i.e., PHB, polyhydroxyvalerate, i.e.,PHV and copolymers or a combination of PHB and PHV (availablecommercially as Biopol), polycaprolactone (available commercially asCapronor), polyanhydrides (aliphatic polyanhydrides in the back bone orside chains or aromatic polyanhydrides with benzene in the side chain),polyorthoesters, polyaminoacids (e.g., poly-L-lysine, polyglutamicacid), pseudo-polyaminoacids (e.g., with back bone of polyaminoacidsaltered), polycyanocrylates, or polyphosphazenes. As used herein, theterm “bio-resorbable” includes a suitable bio-compatible material,mixture of materials or partial components of materials being degradedinto other generally non-toxic materials by an agent present inbiological tissue (i.e., being bio-degradable via a suitable mechanism,such as, for example, hydrolysis) or being removed by cellular activity(i.e., bioresorption, bioabsorption, or bioresorbable), by bulk orsurface degradation (i.e., bioerosion such as, for example, by utilizinga water insoluble polymer that is soluble in water upon contact withbiological tissue or fluid), or a combination of one or more of thebio-degradable, bio-erodable, or bio-resorbable materials noted above.

Two factors are believed to determine the rate of hydrolysis ofsynthetic bio-resorbable materials; the molecular weight and morphologyof the polymer. Thus, by selecting among the available bio-resorbablematerials and setting the thickness of the structure, the endurance ofthe bio-resorbable structure (i.e., the time in the body before thematerial fails under the loads applied by filter members) can becontrolled. Additionally, hydrolytic degradation can be delayed bycoating the surface of the bio-resorbable structure, such as with ahydrophobic layer formed of, for example, a copolymer of lactide,glactide and calcium stearate, which forms an absorbable, adherent,non-flaking lubricant which repels water and slows absorption, therebyimproving retention of tensile strength. Additionally, the coating maybe of a chemical structure that degrades, such as by breaking polymerchains to increase porosity, when exposed to sufficiently energeticradiation, such as ultraviolet light, or laser light of about 800nanometers where the mammalian tissue is generally transparent to suchwavelengths, so that the laser light can be used to degrade the coatingwithout the need for an invasive procedure.

After a period of time, such as a few days to weeks, and typically lessthan 60 days, the bio-resorbable cover material 41 is sufficientlyweakened by enzymatic or hydrolytic degradation that the tips of theretainers 40 will push through the cover material 41. With the tipsuncovered, the retainers 40 may begin penetrating the endothelial layer,becoming lodged in the vessel wall 17.

In a preferred embodiment illustrated in FIG. 12, the entire retainer 40may be formed with a cross section throughout its length which is lessthan that of the anchor members 30 or locator members 20. The primaryobjective of the retainers 40 is to ensure that the filter does notmigrate during normal respiratory function or in the event of a massivepulmonary embolism. The retainer thickness may be sized such that it isof sufficient stiffness when the anchor members 30 are expanded topermit the returner 40 to penetrate the blood vessel wall. However, whenthe filter is to be withdrawn from the vessel wall, withdrawal force inthe direction of blood flow will cause flexure in the retainer so thatthe tip moves toward a position parallel with the axis A (i.e., the hookstraightens). With the retainers so straightened, the filter can bewithdrawn without tearing the vessel wall while leaving only smallpunctures. In one embodiment, the anchor member 30 preferably has across sectional area of about 0.00013 squared inches, and the retainer40 has a cross sectional area preferably of about 0.000086 squaredinches. Since Nitinol is also subject to stress sensitivity that cancause the material to undergo a phase transformation from the austeniticto the martensitic state while the temperature of the material remainsabove the transition temperature, the reduced cross section of theretainer 40 may transition to the martensitic state when subjected to aretraction stress, thus facilitating straightening. A preferred hookembodiment is shown and described in PCT International Application No.PCT/US06/017889, entitled “Removable Embolus Blood Clot Filter,” filedMay 9, 2006, which is incorporated by reference in its entirety herein.

In a further embodiment, a method of implanting a filter 10 in a bloodvessel is provided. In this method, a clinician delivers a filter withretainers on its locator members covered with bio-resorbable material,as described herein, to a desired location in the blood vessel bypushing it through a catheter positioned in the vessel. The filter maybe pushed through and out of the catheter by a push wire. Suitabledelivery systems and methods are described, for example, in U.S. Pat.No. 6,258,026, which is incorporated by reference in its entiretyherein, as well as in PCT International Application No. PCT/US06/17890,entitled “Embolus Blood Clot Filter and Delivery System,” filed on May9, 2006 which is also incorporated by reference in its entirety.

Once positioned in a blood vessel, the bio-resorbable materialencapsulating the hooks is exposed to blood. After a period of time,exposure to blood leads to enzymatic or hydrolytic degradation of thebio-resorbable structure. Due to this degradation, the bio-resorbablematerial breaks down and is assimilated by the body, uncovering thehooks and allowing them to penetrate the walls of the blood vessel.

In the various embodiments, bio-resorbable material covers all or aportion of the retainers 40 until after the filter has been in the bloodvessel for a predetermined period of time, thereby providing a means fordelayed anchoring of at least a portion of the filter. This delayedanchoring (i.e. delayed retainer deployment) may be accomplished usingany of the techniques described herein or their equivalents. The periodof time for uncovering the hooks may be predetermined by adjusting thevolume of bio-resorbable material over the retainer tips and/or byfurther coating the surface of the bio-resorbable material with asubstance or material that resists water penetration for a period oftime, thereby delaying onset of the resorption process.

Further control over the period of time after delivery that the hooksremain covered may be achieved using a suitable material that changeschemical structure upon exposure to a particular activating wavelengthof radiation (e.g., UV or visible light). In one embodiment, thebio-resorbable cover material 41 is provided with a water repellantcoating that prevents body fluids from degrading the resorbablematerial. Once exposed to the activating wavelength of radiation, thewater repellant coating dissolves or becomes porous so that hydrolyticor enzymatic degradation of the underlying resorbable material canbegin. In another example, exposure to a specific wavelength of lightcauses a light-activated material to change structure and thereby createseparation between the cover material 41 and retainer 40. In an example,the activating radiation can be UV light, visible light or near infraredlaser light at a wavelength (e.g., 800 nanometers) at which tissues aresubstantially transparent to such wavelength. In a particularembodiment, the coating material may be polyethylene with a meltingpoint of about 60 degrees Celsius mixed with biocompatible dyes thatabsorb radiation in the 800 nm range, such as indocyanine green (whichabsorbs radiation around 800 nm and is biocompatible). Biocompatibledyes such as indocyanine green will absorb the light energy, therebyraising the temperature in the polymer to about 60 degrees Celsius orhigher. When the melting point temperature, e.g., 60 degrees Celsius, isreached the polymer structurally weakens thereby causing the coating tolose integrity (i.e., crack, peal or otherwise become porous or at leasta portion of the surface).

Several aspects of the various embodiments provide advantages over theknown filters. For example, the capability of enabling locator membersto also anchor the filter in a blood vessel is desirable, and theability to immediately withdraw a filter from a patient without damagingthe patient's blood vessels, since anchoring hooks are initiallycovered, may provide treatment advantages not available with knownfilters.

In addition to the foregoing embodiments, the bio-resorbable materialcovering all or a portion of the hooks may be employed with bloodfilters configured to be removable. An example of a removable filterembodiment is illustrated in FIG. 15. Further description of a removablefilter is provided in PCT International Application No. PCT/US06/017889,entitled “Removable Embolus Blood Clot Filter”.

Referring to FIG. 5, a filter 10 is illustrated in a perspective view.The filter 10 includes a hub 12, locator members 20, and anchor members30 that have a hook 40. The filter 10 can be made from a plurality ofelongate wires, which are preferably metal, such as, for example,Elgiloy® and more preferably a super-elastic shape memory alloy, such asNitinol. The shape memory alloy can further be defined as preferablyhaving an austenite finish (A_(f)) temperature below body temperature.The wires are joined at the filter trailing end by a hub 12 using asuitable connection technique, such as, for example, welding, laserwelding, or plasma welding or being bonded together. Preferably, thewires are plasma welded. As used herein, “wire” refers to any elongatedmember of narrow cross section, including rods, bars, tubes, ribbon andnarrow sections cut from thin plate, and is not intended to limit thescope of the invention to elongated members of circular cross section,cut from wire stock or manufactured according to a particular method ofmetal forming.

Each locator member 20 has a proximal locator end 20P and a distallocator end 20D. Similarly, each anchor member 30 has a proximal anchorend 30P and a distal anchor end 30D. The distal anchor end 30D may beprovided with a hook 40, details of which are shown in FIG. 12.

Referring to FIGS. 8 and 9, the locator member 30 may be comprised of aplurality of locator segments, preferably between 3 and 6 segments andmore preferably four locator segments LS1, LS2, LS3, and LS4. Firstlocator segment LS1 may be a curved portion extending away from the hub12 in a first direction along the longitudinal axis A. The secondlocator segment LS2 may extend generally linearly along a second axis110; third locator segment LS3 extends generally linearly along a thirdaxis 120; and the fourth locator segment LS4 extends generally linearlyalong a fourth axis 130 (or is configured as a hook as described below).In an embodiment, the various axes A, 110, 120, 130, and 140 aredistinct from one another in that each may intersect with one anotherbut none of them are substantially collinear with each other.

The locator segment LS2 may be distinct from locator segment LS3 byvirtue of a joint or bend ill. The locator segment LS3 may be distinctfrom locator segment LS4 via a joint or bend LJ2. The joint or bend LJIor LJ2 can be viewed as a location formed by the intersection of thesegments defining a radiused portion connecting any two segments. In onepreferred embodiment, the locator member tip segment LS4 is configuredas a hook for hooking into the endothelial layers of the blood vesselwall. Such hooks may be of the basic configuration illustrated in FIG.12, or other configurations. As described above, embodiments featuringhooks on the locator members will include a bio-resorbable covermaterial 41, as illustrated in FIG. 13, to permit the locator members toglide easily over the endothelial layer during the initial positioningmovements of the filter delivery procedure. As seen in FIGS. 1A, 1C, 2,3A, 3B, 4, 13, 14, and 15, the bio-resorbable cover material 41 may havea rounded bead shape.

The number of locator members 20 may range from three to twelvelocators. The filter embodiment illustrated in FIG. 8 includes sixlocators that are preferably generally equiangularly spaced about axisA. In the embodiment illustrated in FIG. 9, locator segment LS1 extendsthrough an arc with a radius of curvature R₁ whose center may be locatedalong an axis orthogonal to axis A over a radially transverse distanced₃ and over a longitudinal distance L₄ as measured from a terminalsurface 11 of the hub 12 along an axis generally parallel to thelongitudinal axis A. The locator segment LS2 extends along axis 110 toform a first angle θ₁ with respect to the longitudinal axis A whereasthe locator segment LS3 extends along axis 120 to form second angle θ₂.As shown in FIG. 9, the first locator joint or bend LJ1 may be locatedat a longitudinal length L₁ generally parallel to axis A from theterminal surface 11. The first locator joint or bend LJ1 may be alsolocated at a distance of about one-half distance d₁ from axis A on agenerally orthogonal axis with respect to axis A as shown in FIG. 9,where the distance d₁ is the distance between inside facing surfaces ofrespective diametrically disposed locators 20. The second locator jointLJ2 may be located over a longitudinal length L₂ generally parallel toaxis A. The second locator joint LJ2 may be located over a distance ofabout one-half diameter d₂ from axis A. The distance d₂ is the distancebetween the outermost surface of the fourth segment LS4 of respectivediametrically disposed locators 20. The thickness of locator member 20is t₁. Where the locator member 20 is preferably a wire of circularcross section, the thickness t₁ of the locator 20 may be the diameter ofthe wire.

A range of values may be used for the aforementioned dimensionalparameters in order to provide locator members that will locate thefilter within the vein or vessel in which the filter is to be applied ina manner that positions segment LS4 approximately parallel to the wallsof the vein or vessel and provides sufficient lateral force against thevein or vessel wall for positioning but not so much force as to causeinjury to the wall. In embodiments where the locator member tip segmentLS4 is configured as a hook, the dimensional parameters will be set soas to apply sufficient force to the hooks to drive the tip into thevessel wall after the bio-resorbable cover material 41 has beenresorbed.

For example, a filter intended to be placed in a narrow vein or vessel,such as a human infant or canine vena cava, may have smaller dimensionsL₁, L₂, L₃, L₄, LS1, LS2, LS3, LS4, d₁ and d₂ than a filter intended tobe placed in a large vein or vessels, such as an adult human vena cavaor femoral vein. Reducing these dimensions will facilitate completedeployment of the locator members so they can accomplish their intendedpositioning and filtering functions. In an example embodiment suitablefor an adult human vena cava filter, when the filter is at thetemperature of the subject and unconstrained, the radius of curvature R₁is about 0.02 inches with the center of the radius R₁ being located overa distance d₃ from the axis A of about 0.1 inches and length L₄ of about0.2 inches; the length L₁ may be about 0.3 inches; length L₂ may beabout 0.9 inches; distance d₁ (as measured to the inside facing surfacesof diametrically disposed locators 20) may be about 0.8 inches; distanced₂ may be about 1.3 inches; the first angle θ₁ may be about 58 degrees,the second angle θ₂ may be about 22 degrees; and the thickness t₁ of thelocator may be about 0.013 inches. It should be noted that the valuesgiven herein are approximate, representing a dimension within a range ofsuitable dimensions for the particular embodiment illustrated in thefigures, and that any suitable values can be used as long as the valuesallow the filter to function as intended in a subject's blood vessel.

Referring to FIG. 11, the filter hub 12 may be provided with an internalcylindrical opening with a diameter of about two times the distance d₈.Referring now to FIG. 10 and FIG. 11, each of the plurality of anchormembers 30 may be provided with a first anchor segment LA1, a portion ofwhich is disposed within the hub 12, connected to a second anchorsegment LA2 by a first anchor joint or bend AJ1, which may be connectedto a third anchor segment LA3 via a second anchor joint or bend AJ2. Thethird anchor segment LA3 may be connected to the hook 40 via thirdanchor joint or bend AJ3. The first anchor segment LA1 preferablyextends obliquely with respect to axis A. The second anchor segment LA2preferably extends along axis 130 oblique with respect to the axis Aover an angle θ₃ with respect to the longitudinal axis A. The thirdanchor segment LA3 preferably extends along axis 140 oblique withrespect to the longitudinal axis A over an angle θ₄. The second anchorjoint or bend AJ2 can be located at a sixth longitudinal distance L₆ asmeasured on an axis generally parallel to the axis A from the terminalsurface 11 of the hub 12 and at about one half the fourth distance d₄ asmeasured between generally diametrical end points of two anchors 30 onan axis generally orthogonal to the axis A. The third anchor joint AJ3may be located at a seventh longitudinal distance L₇ as measured alongan axis generally parallel to axis A and at a transverse distance ofabout one-half distance d₁ as measured on an axis orthogonal to the axisA between the inner surfaces of two generally diametric anchors 30. Thethickness of anchor member 30 is nominally t₂. Where, for example, theanchor member 30 is preferably a wire of circular cross section, thethickness t₂ of the anchor 30 may be the diameter of the wire. As shownin FIG. 11, the hook 40 may be contiguous to a plane located at alongitudinal distance L₁₀ as measured to the terminal surface 11 of hub12. The hook 40 may be characterized by a radius of curvature R₂, in itsexpanded configuration at a suitable temperature, e.g., room temperatureor the internal temperature of a subject. The center of the hookcurvature R₂ can be located at a distance L₁₁ as measured along an axisgenerally parallel to the axis A from the terminal surface 11 of hub 12and at one-half distance d₆ as measured between two generallydiametrical hooks 40. The tips 40T of respective diametric hooks 40 maybe located at longitudinal distance L₁₂ (which may be approximately thesame as longitudinal distance L₇ to the third anchor joint AJ3) and atone half of distance d₇ between diametric hooks 40.

A range of values may be used for the aforementioned dimensionalparameters in order to provide anchor members that will locate andanchor the filter within the vein or blood vessel in which the filter isto be applied in a manner that positions hooks 40 in contact with thewalls of the vein or blood vessel and provides sufficient lateral forceagainst the wall to ensure the hooks engage the wall (e.g., penetratingthe endothelium) but not so much force as to cause injury to the wall.For example, a filter intended to be placed in a narrow vein or vessel,such as a child or dog vena cava, may have smaller dimensions than afilter intended to be placed in a large vein or vessels, such as anadult vena cava or femoral vein, so that the anchor members can deploysufficiently to accomplish the positioning, anchoring and filteringfunctions. In an example embodiment suitable for an adult human venacava filter, when the filter is at the temperature of the subject andunconstrained, the longitudinal distance or axial length L₈ of the firstanchor segment LA1 may be about 0.02 inches; the longitudinal distanceL₉ between the second and third anchor joints AJ2, AJ3 may be about 0.2inches; L₁₀ may be about 1.4 inches; L₁₁ may be about 1.4 inches; d₅ maybe about 1.5 inches; d₇ may be about 1.6 inches; d₈ may be about 0.01inches; d₆ may be between 1.5 and 1.6 inches; L₁₂ may be about 1.4inches; the radius of curvature R₂ may be about 0.03 inches; and thethickness t₂ of the anchor member may be about 0.013 inches. Mostpreferably, a very small radius of curvature R₃ characterizes anchorjoint or bend AJ2 where R₃ may be about 0.01 inches.

Referring to FIG. 12, the hook 40 may be provided with a proximal hookportion 40P and a distal hook portion 40D on which a sharpened tip 40Tis provided. The hook 40 may be formed to have a thickness t₃. Where thehook 40 is formed from a wire having a generally circular cross-section,the thickness t₃ may be generally equal to the outside diameter of thewire. In an embodiment, the hook thickness t₃ is approximately 0.8 thatof the anchor thickness t₂. The wire may be configured to follow aradius of curvature R₂ whose center may be located at longitudinaldistance L₁₁ and radial distance d₆ when the filter is at thetemperature of a subject, as discussed above. The tip 40T may beprovided with a generally planar surface 40D whose length may beapproximately equal to length h₁. The planar surface length h₁ can beabout 0.02 inches. The tip 40T may be located over a distance h₂ from aplane tangential to the curved portion 40S. The tip distance h₂ can beabout 0.05 inches.

The material for the filter may be any suitable bio-compatible materialsuch as, for example, polymer, memory polymer, memory metal, thermalmemory material, metal, metal alloy, or ceramics. Preferably, thematerial may be Elgiloy®, and most preferably Nitinol, which is athermal shape memory alloy.

The use of a thermal shape memory material, such as Nitinol, for thelocator and anchor members facilitates collapsing the filter radiallyinward from its normally expanded (i.e., unconstrained) configurationtoward its longitudinal axis into a collapsed configuration forinsertion into a body vessel.

Although the filters of the various embodiments are preferably formedfrom a temperature-responsive shape memory or super-elastic material,such as Nitinol, they can also be formed of a compressible spring metalsuch as stainless steel or a suitable plastic.

The structure of the hooks 40 is believed to be important in resistingmigration of the filter once installed while allowing for removal fromthe blood vessel after installation. As in the case of hooks formed onthe anchor members of known permanent vena cava filters, these hooks 40penetrate the vessel wall when the filter 10 is expanded to anchor thefilter in place and prevent filter migration longitudinally within thevessel in either direction. However when the hooks 40 are implanted andsubsequently covered by the endothelium layer, they and the filter canbe withdrawn without risk of significant injury or rupture to the venacava. Minor injury to the vessel wall due to hook withdrawal such asdamage to the endothelial layer or local vena cava wall puncture isacceptable.

To permit safe removal of the filter, the juncture section 40S may beconsiderably reduced in cross section relative to the thickness t₂ orcross section of the anchor member 30 and the remainder of the hook 40.The juncture section 40S may be sized such that it is of sufficientstiffness when the anchor members 30 are expanded to permit the hook 40to penetrate the blood vessel wall. However, when the hook is to bewithdrawn from the vessel wall, withdrawal force in the direction ofblood flow BF will cause flexure in the juncture section 40S so that thehook tip 40T moves toward a position parallel with the axis A (i.e., thehook straightens). With the hooks generally straightened as such (butnot quite fully), the filter can be withdrawn without tearing the vesselwall while leaving only small punctures. In one embodiment, the anchormember 30 has a cross sectional area of about 0.00013 squared inches,and the hook 40, particularly the curved juncture section 40S has across sectional area of about 0.000086 squared inches.

With reference to FIG. 12, it will be noted that the entire hook 40 canbe formed with a cross section t₃ throughout its length that is lessthan that of the locator members 20 (which have thickness t₁) or anchormembers 30 (which have thickness t₂). As a result, an axial withdrawalforce will tend to straighten the hook 40. This elasticity in the hookstructure prevents the hook from tearing the vessel wall duringwithdrawal. The force required to cause opening of the hooks 40 can bemodulated to the total force required to resist filter migration. Thisis accomplished by changing the cross sectional area or geometry of thehooks, or by material selection, as discussed above.

By reducing the cross sectional area of a portion or all of the hooks 40relative to that of the anchor members 30 or locator members 20, stresswill be concentrated in the areas of reduced cross section whenlongitudinal force is applied to the hub 12 in the direction of bloodflow BF (i.e., towards the hub 12 of the filter) such as to remove thefilter. Under this concentrated stress, the reduced cross sectionportions of the hooks may transition to the martensitk state, therebybecoming elastic so that they straighten.

In an embodiment, each hook must be capable of resisting approximatelyat least 70 grams of force for the filter 10 to resist at least 50 mmHgpressure gradient in a 28 mm diameter vessel. To prevent excessivevessel trauma each individual hook needs to be relatively weak. Bybalancing the number hooks and the individual hook strength, minimalvessel injury can be achieved while still maintaining the at least 50mmHg pressure gradient criteria, or some other predetermined pressuregradient criteria within a range of from about 10 mmHg to 150 mmHg.

In a further embodiment of the removable filter illustrated in FIG. 14,the hooks on the anchor members may also be encompassed or covered witha bio-resorbable cover material 41 so that when the filter is firstdelivered into a blood vessel, the anchors deploy without driving thehooks into the vessel wall. This embodiment may be employed on filterswith locator members also having hooks, as illustrated in FIG. 14, andlocator members without hooks. As with the previously describedembodiments, after the filter has been in the blood vessel for a periodof time, the cover material 41 is resorbed, thereby uncovering theanchor hooks, allowing them to penetrate the vessel wall to prevent thefilter from being dislodged by blood flow. This embodiment has theadvantage of allowing the filter to be removed within a predeterminedperiod of time after delivery without damaging the endothelial layers ofthe blood vessel.

Instead of the hub 12 provided in the above described embodiments, aretrieving hook 220 can be provided as part of filter device 200, as inthe embodiment shown in FIG. 15. The filter embodiment 200 preferablyincludes a hub 210 with a retrieving hook 220. Providing a retrievinghook 220 on the filter facilitates removal of the filter from a bloodvessel, such as by means of a wire snare introduced through a removalcatheter. Including the retrieval hook 220 on a filter whose retainersare covered by a bio-resorbable material 41, as illustrated in FIG. 15,permits a clinician to readily remove a filter soon after deliverywithout traumatizing the blood vessel. In this embodiment, the covermaterial 41 prevents the retainers, preferably configured as hooks, fromengaging the blood vessel wall for a predetermined period of time andthe retrieval hook 220 of the hub 210 facilitates capturing andretrieving the filter via a catheter. While FIG. 15 shows cover material41 on both locator and anchor member hooks, the cover material may beapplied only to the locator member hooks, or only to the anchor memberhooks or to a combination of some locator hooks and some anchor memberhooks as part of this embodiment.

Referring to FIGS. 16-19, the retrieving hook 220 is configured to beeasily captured by a snaring device used to retrieve the filter 200 froma subject. Referring to FIGS. 16 and 17, the retrieving hook 220 can beformed as a monolithic member 230 with the hub 210 or as a separatemember joined to the hub 210 by a suitable technique, such as, forexample, laser welding, plasma welding, brazing, welding, soldering, orbonding. In a preferred embodiment, the member 230 may be a machinedbillet member with a blind bore 240 formed through a portion of the hub210. The hook portion 220 preferably includes ramped surfaces 250 and260 that are believed to be advantageous in allowing the filter 200 tobe retrieved without binding at the catheter opening due to an offsetentry position of the filter 200. In other words, there may becircumstances during removal procedures where the axis 300 of the member230 is not generally parallel or aligned with a longitudinal axis of thecatheter retrieving device. In such cases, the greater the retentionforce, it is believed that the greater the likelihood of the hook beingsnagged on the catheter inlet opening thereby complicating the filterretrieval process. By virtue of the ramps 250 and 260, it is believedthat binding or snagging is substantially reduced. In particular, asshown in FIGS. 18 and 19, the ramp 250 includes a radius of curvature R₄coupled to a first flat portion 252 and a second flat portion 254. Theflat portion 254 can be coupled to a hook portion 220 which has aradiused surface R₆. As shown in FIG. 18, the first flat portion 252 ispreferably coupled to another radiused portion R₇.

Bio-active agents can be incorporated with the bio-resorbable coveringmaterial in the various embodiments. Such bio-active agents include (butare not limited to) pharmaceutic agents such as, for example,anti-proliferative/antimitotic agents including natural products such asvinca alkaloids (i.e. vinblastine, vincristine, and vinorelbine),paclitaxel, epidipodophyllotoxins (i.e. etoposide, teniposide),antibiotics (dactinomycin (actinomycin D) daunorubicin, doxorubicin andidarubicin), anthracyclines, mitoxantrone, bleomycins, plicamycin(mithramycin) and mitomycin, enzymes (L-asparaginase which systemicallymetabolizes L-asparagine and deprives cells which do not have thecapacity to synthesize their own asparagine); antiplatelet agents suchas G(GP) IIb/IIIa inhibitors and vitronectin receptor antagonists;anti-proliferative/antimitotic alkylating agents such as nitrogenmustards (mechlorethamine, cyclophosphamide and analogs, melphalan,chlorambucil), ethylenimines and methylmelamines (hexamethylmelamine andthiotepa), alkyl sulfonates-busulfan, nirtosoureas (carmustine (BCNU)and analogs, streptozocin), trazenes—dacarbazinine (DTIC);anti-proliferative/antimitotic antimetabolites such as folic acidanalogs (methotrexate), pyrimidine analogs (fluorouracil, floxuridine,and cytarabine), purine analogs and related inhibitors (mercaptopurine,thioguanine, pentostatin and 2-chlorodeoxyadenosine {cladribine});platinum coordination complexes (cisplatin, carboplatin), procarbazine,hydroxyurea, mitotane, aminoglutethimide; hormones (i.e. estrogen);anti-coagulants (heparin, synthetic heparin salts and other inhibitorsof thrombin); fibrinolytic agents (such as tissue plasminogen activator,streptokinase and urokinase), aspirin, dipyridamole, ticlopidine,clopidogrel, abciximab; antimigratory; antisecretory (breveldin);anti-inflammatory: such as adrenocortical steroids (cortisol, cortisone,fludrocortisone, prednisone, prednisolone, 6α-methylprednisolone,triamcinolone, betamethasone, and dexamethasone), non-steroidal agents(salicylic acid derivatives i.e. aspirin; para-aminophenol derivativesi.e. acetominophen; indole and indene acetic acids (indomethacin,sulindac, and etodalac), heteroaryl acetic acids (tolmetin, diclofenac,and ketorolac), arylpropionic acids (ibuprofen and derivatives),anthranilic acids (mefenamic acid, and meclofenamic acid), enolic acids(piroxicam, tenoxicam, phenylbutazone, and oxyphenthatrazone),nabumetone, gold compounds (auranofin, aurothioglucose, gold sodiumthiomalate); immunosuppressives: (cyclosporine, tacrolimus (FK-506),sirolimus (rapamycin), azathioprine, mycophenolate mofetil); angiogenicagents: vascular endothelial growth factor (VEGF), fibroblast growthfactor (FGF); angiotensin receptor blockers; nitric oxide donors;anti-sense oligionucleotides and combinations thereof; cell cycleinhibitors, mTOR inhibitors, and growth factor receptor signaltransduction kinase inhibitors; retenoids; cyclin/CDK inhibitors; HMGco-enzyme reductase inhibitors (statins); and protease inhibitors.

Although the preferred embodiments of the invention have been shown anddescribed in relation to the filters of FIGS. 2 and 5, other filters canalso be utilized such as, for example, commercially available filtersthat include a retainer as part of their overall design.

While the present invention has been disclosed with reference to certainpreferred embodiments, numerous modifications, alterations, and changesto the described embodiments are possible without departing from thesphere and scope of the present invention. Accordingly, it is intendedthat the present invention not be limited to the described embodiments,but that it have the full scope defined by the language of the followingclaims, and equivalents thereof.

What is claimed is:
 1. A filter to be placed in a blood vessel, thefilter comprising: a) a plurality of appendages, each appendage havingan anchor member with a distal end sharp tip; b) a bio-resorbable massof material that encapsulates the distal end sharp tip, wherein wheninitially placed in a patient's vessel said mass of material has anouter surface that is smooth for enabling the mass of material to slidealong the inside of the vessel; c) wherein when in use in said patient'svessel, the bio-resorbable mass of material that encapsulates the distalend sharp tip of at least one of the plurality of appendages resorbsafter time and allows the distal end sharp tip to engage the vessel; d)a hub coupled to the plurality of appendages, the plurality ofappendages further comprising a plurality of locator members that locatethe filter with respect to a wall of the blood vessel; e) a plurality ofanchor members coupled to the hub, at least one of the plurality ofanchor members having a retainer configured to penetrate a wall of theblood vessel when the filter is disposed in the blood vessel, wherein f)a rounded bead shaped bio-resorbable mass of material that encompassesat least a portion of the retainer of the at least one of the pluralityof anchor members; g) the retainer is held by the mass of bio-resorbablematerial in a first position wherein the rounded bead shaped mass ofmaterial is able to slide along the vessel wall, said retainer moving toa second position when the bio-resorbable material resorbs; and h)wherein the first and second positions have different curvatures for theretainer.
 2. The filter of claim 1, wherein the bio-resorbable mass ofmaterial is coated by a water repellant coating.
 3. The filter of claim2, wherein the water repellant coating is activated by radiation tobecome at least partially porous.
 4. The filter of claim 3, wherein thewater repellant coating is activated by radiation having a wavelength ofapproximately 800 nm.
 5. The filter of claim 1, wherein the anchormember has a hook shape in said second position.
 6. A filter to beplaced in a blood vessel, the filter comprising: a) a plurality ofappendages, each appendage having an anchor member with a distal endsharp tip; b) a bio-resorbable mass of material that encapsulates thedistal end sharp tip, wherein when initially placed in a patient'svessel said mass of material has an outer surface that is smooth forenabling the mass of material to slide along the inside of the vessel;c) wherein when in use in said patient's vessel, the bio-resorbable massof material that encapsulates the distal end sharp tip of at least oneof the plurality of appendages resorbs after time and allows the distalend sharp tip to engage the vessel; d) a hub disposed along alongitudinal axis, the hub being coupled to the plurality of appendages;e) wherein the appendages are each coupled to the hub, each anchormember including a retainer spaced along the longitudinal axis from thehub at a first longitudinal distance, and radially spaced apart from thehub at a first longitudinal distance, and radially spaced from thelongitudinal axis a first radial distance, each curved anchor memberbeing configured to penetrate a wall of the blood vessel when the filteris disposed in the blood vessel; and f) wherein the plurality ofappendages comprise a plurality of locator members, each locator memberincluding: a first portion proximate the hub; a second portion thatextends from the first portion along a first axis; a third portion thatextends from the second portion along a second axis distinct from thefirst axis; and g) the bio-resorbable mass of material encompasses atleast a portion of the retainer of the at least one of the plurality ofanchor members; h) the retainer is held by the mass of bio-resorbablematerial in a first position, moving to a second position when thebio-resorbable material resorbs; and i) wherein the first and secondpositions have different curvatures for the retainer.
 7. The filter ofclaim 6, wherein: the second portion extends from the first portion afirst length along the first axis, which is oblique with respect to thelongitudinal axis; and the third portion extends a second length alongthe second axis, wherein the second length is greater than the firstlength, and the second axis is oblique with respect to the longitudinalaxis.
 8. The filter of claim 6, wherein the first portion of each of theplurality of locator members includes a curved portion defining a radiusof curvature, the first portion forming a first angle with respect tothe longitudinal axis.
 9. The filter of claim 8, wherein the first axisdefines a second angle with respect to the longitudinal axis, the secondaxis defines a third angle with respect to the longitudinal axis, thefirst angle being greater than each of the second and third angles. 10.A filter to be placed in a patient's blood vessel, the filtercomprising: a) a plurality of appendages, at least some of theappendages having an anchor member with a distal end sharp tip; b) arounded bead shaped bio-resorbable mass of material that encapsulatesthe distal end sharp tip, wherein said mass of material has an outersurface that is smooth for enabling the mass of material to slide alongthe inside of the vessel; and, c) a hub disposed along a longitudinalaxis, the hub being coupled to the plurality of appendages; d) whereinthe appendages are each coupled to the hub, each anchor member spacedalong the longitudinal axis from the hub at a first longitudinaldistance, and radially spaced from the longitudinal axis a first radialdistance, each anchor member distal end sharp tip being configured topenetrate a wall of the blood vessel when the filter is disposed in theblood vessel; and e) wherein when in use in the vessel, thebio-resorbable mass of material initially encapsulates the distal endsharp tip of at least one of the plurality of appendages and laterresorbs after time and allows the distal end sharp tip to engage thevessel; and f) wherein the plurality of appendages comprise a pluralityof locator members, each locator member including: a first portionproximate the hub; a second portion that extends from the first portionalong a first axis; and a third portion that extends from the secondportion along a second axis distinct from the first axis; and, g)wherein each of the plurality of anchor members includes a first portionproximal the hub and a second portion distal the hub, each of the firstand second portions of the anchor members being generally linear anddisposed on distinct axes each oblique to the longitudinal axis, whereinthe first portion of the anchor members is longer than the secondportion of the anchor members and each of the plurality of anchormembers is coupled to the second portion of the locator members.
 11. Thefilter of claim 10, wherein each of the plurality of anchor members isoffset in alignment with respect to the axis on which at least oneportion of the corresponding, anchor member is aligned.
 12. The filterof claim 10, wherein: a) the first portion of each of the plurality ofanchor members extends away from the longitudinal axis at a fourthangle; b) the second portion of each of the plurality of anchor membersextends away from the longitudinal axis at a fifth angle; and c) thefourth angle is less than the fifth angle.
 13. The filter of accordingto claim 10, wherein each distal end sharp tip of the plurality ofappendages comprises a hook having a curved configuration in anoperative condition and a generally linear configuration in aconstrained condition.
 14. The filter of claim 10, wherein the hubcomprises a retrieving hook.
 15. The filter of claim 10, a) wherein thefirst portion includes a curved portion defining a radius of curvatureof about 0.02 inches, the first portion extending to a point radiallyabout 0.4 inches from the longitudinal axis and axially about 0.3 inchesfrom the hub; b) the second portion of each of the plurality of locatormembers extends to a point radially about 0.75 inches from thelongitudinal axis and axially about 0.9 inches from the hub; and c)wherein at least one hook of the plurality of anchor members includes aportion being radially about 0.75 from the longitudinal axis and axiallyabout 1.3 inches from the hub, each of the plurality of anchor memberincludes a hook defining a radius of curvature of about 0.03 inches andhaving a tip portion defining an axial length of about 0.05 inches. 16.The filter of claim 10, wherein at least one of the plurality of locatormembers and the plurality of anchor members comprises at least one of ahook, a projection oblique to the locator member, a barb disposed on thelocator member, or a tip having two barbs extending therefrom.
 17. Thefilter of claim 10, wherein at least one of the plurality of locatormembers and the plurality of anchor members comprises a curved hookhaving a deformed configuration so as to be generally linear, the hookbeing covered by the bio-resorbable material to maintain the hook in thedeformed configuration.